Internal combustion engines are typically protected from acquiring dust and debris in the intake combustion air by the presence of an air filter or air cleaner in the air intake tract. When operated in dusty or particulate debris laden environments, dust and debris can quickly accumulate in the air cleaner. Further movement of the debris is blocked by the filtering activity of the air filter, and so accumulated debris must be removed to prevent obstruction of the air cleaner filter element.
As the engine draws combustion air through the intake tract and air cleaner, the air cleaner operates at a slight vacuum relative to outside air pressure. This vacuum works against urging dust and debris to exit the air cleaner through the dust valve as the vacuum will tend to draw dust and debris back into the air cleaner rather than permitting the debris to exit to the outside.
Various types of flap valves are applied as dust valves in the prior art. These valves have lips that are held closed by the vacuum and may be responsive to pressure pulsations in the intake tract, as due to the operation of the engine. In response to momentary pressure fluctuations, such flap valves may momentarily open to discharge dust from within the air cleaner into the environment. If the pressure pulsations are insufficient or the vacuum too strong to permit the flap valve lips to open, then some varieties of the flap valves will open when the engine is shutdown and the vacuum is thereby removed. If the flap valve fails to reliably periodically open (perhaps due to the operating vacuum, insufficient engine air intake pressure pulsations, elastomeric aging or other issues), then dust accumulates in the air cleaner and air filter obstruction is not avoided.
With the advent of tier 4 emission standards, engine manufacturers are providing designs that have a steadier air intake pressure and reduce pressure pulsations; therefore engine intake air pressure pulsations may be insufficient to operate dust removal flap valves and the like.
Additionally the elastomers of elastomeric dust valves can age, lose their resilience or even disintegrate and therefore fail to close or close fully during operation. This is undesirable as drawing outside air in the reverse direction through the dust valve can draw in outside dust and debris and, due to the vacuum in the air intake tract, prevent accumulated debris in the air cleaner or intake tract from being expelled to the environment.
Therefore, there remains a need in the art for a dust valve that avoids elastomeric aging issues, is low in cost, prevents back-flow through the dust valve, is self actuating and is able to eject dust while operating against intake tract vacuum.